Magnetostrictive actuators are generally known in the art, as disclosed for example in U.S. Pat. No. 5,451,821 to Teter et al. Such an actuator having a magnetostrictive rod as its active component is provided with magnetic field bias adjustment to optimize operation for single fixed external loads. It is therefore an important object of the present invention to provide the foregoing type of magnetostrictive actuator with means for optimizing the operating characteristics thereof in accordance with ambient variation of loading, such as external pressures applied for example to sonar transducer types of actuators associated with marine vessels during travel through pressure exerting water between shallow and deep water depths.